1. Field of the Invention
The present invention relates to telecommunications networks and more particularly to telecommunications networks of the kind having service switching points with local software control arrangements and service control points to which the local software control arrangements may apply for instructions on handling (eg) number translation functions.
2. Related Art
Telecommunications networks of the kind having service control points in an intelligent overlay layer enable rapid provision of special services to customers without requiring distribution of new software or data to every computer controlled switching point. Thus, in these intelligent networks local processing capability in, for example digital main switching units, may be triggered by the occurrence of certain events to refer to the external intelligence for further instructions on call processing.
For example, when an originating customer dials a code representing a special service rather than a destination switch, triggering of the control processor of the service switching point will result in a signalling message being sent to a remote service control point indicating the code which has been dialled. In the service control point a server will analyse the dialled code and return instructions for call handling to the service switching point. Such instructions may be to allocate a receiver, collect a further `n` digits and report back. Once the further digits have been received the entire process using the whole number may be repeated so that the service control point may now translate the entire received number to a switching destination of the core transport network of the telecommunications system. The service switching point may now switch the call through in accordance with these instructions.
Telemarketing and televoting services in which customers are given a dedicated telephone number to dial in response to advertising or television programs are now well known. It is also known that communications networks may become congested as a result of a mass response to special offers. For example, where a destination telephone number is advertised on a national basis and significant numbers of customers attempt to make a call to the telephone number, a focused overload of calls seeking to use incoming trunks to the destination main switching unit and/or the destination local exchange can result in switch blocking of normal service traffic.
In serious cases of focused overload attempts by other main switching units to communicate with the congested switching unit by using alternative routes may result in the congestion spreading outwards across the network potentially leading to a complete communications freeze. One method of dealing with focused overloads in communications networks is disclosed in our co-pending patent application number GB94/02512 filed under the Patent Co-operation Treaty. In this PCT application there is disclosed a method of restricting calls having a common call identity when the rate at which calls to the destination specified are failing exceeds a predetermined level. This method automatically restricts calls though the transport network to the destination by introducing a gap between successive calls from one originating point. Each originating node may have its own perception of the destination overload such than an imbalance between call completions from one area and call completions from another area occurs.
Once this method of controlling calls to congested destinations is applied in the intelligent network, congestion may also adversely affect access to the service control point. In practice the service control point comprises a number of traffic servers to which originating requests for instructions are distributed. Here, however, each traffic server may develop its own perception of the traffic overload and if the service switching point application from a particular service switching point is handled by a first traffic server and a subsequent application by a different traffic server conflicting call restriction instructions may be returned.